怎么改？

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace LambdaDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("传统的委托代码示例：");
                FindListDelegate();
            Console.WriteLine("\n");
            Console.WriteLine("使用匿名方法的示例：");
                FindListAnonymousMethod();
            Console.WriteLine("\n");
            Console.WriteLine("使用Lambda的示例：");
            FindListLambdaExpression();
        }
        static void FindListDelegate()
        {
            List<string> list = new List<string>();
            list.AddRange(new string[] { "课程", "J2EE课程", "PHP课程", "数据结构课程" });
                Predicate<string>findPredicate=new Predicate<string>(IsBookCategory);
                List<string>bookCategory=list.FindAll(findPredicate);
            foreach(string str in bookCategory)
            {
                Console.WriteLine("{0}\t",str);
            }
        
        }
        static void FindListAnonymousMethod()
        {
            List<string>list=new List<string>();
            list.AddRange(new string[]{"课程","J2EE课程","PHP课程","数据结构课程"});
            List<string>bookCategory=list.FindAll
                (delegate(string str)
                    {
                        return str.EndsWith("课程")?true:false;
                    }
            );
            foreach(string str in bookCategory)
            {
                Console.WriteLine("{0}\t",str);
            }
        }
        static void FindListLambdaExpression()
        {
            List<string> list = new List<string>();
            list.AddRange(new string[] { "课程", "J2EE课程", "PHP课程", "数据结构课程" });
            List<string> bookGategory = list.FindAll((string str)=>str.EndsWith("课程"));
            foreach (string str in bookGategory)
            {
                Console.WriteLine("{0}\t", str);
            }
        }
    }
}

提示错误错误    1    当前上下文中不存在名称“IsBookCategory”      动态网站开发基础教程书中第51页的源代码；请高手指点，如何修改，为什么